Storage system, storage control device, and data relay method using storage control device

ABSTRACT

A plurality of virtual volumes with different control functions are associated with one real volume and remote copying is conducted. A relay system comprises a plurality of virtual volumes V 12,  V 21  mapped to the same real volume R 1.  A virtual volume V 21  for transmission control is mapped to a real volume R 1,  a real volume R 2  is mapped to the virtual volume V 21,  and the virtual volume V 12  for reception control is mapped to the real volume R 2.  If a command is received from a local system  10,  the virtual volume V 12  for reception control writes data into the virtual volume V 21  via the real volume R 2  (virtual entity). The virtual volume V 21  transmits the data to a copy destination volume V 22  and writes the data into the real volume R 1.

CROSS REFERENCES TO RELATED APPLICATION

This application relates to and claims priority from Japanese PatentApplication No. 2003-397380 filed on Nov. 27, 2003, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a storage system, a storage controldevice, and a data relay method using the storage control device.

2. Description of the Related Art

For example, in a database system handling large scale data, such asinformation management systems of data centers or enterprises, the dataare managed by using a storage system configured separately from a hostcomputer. This storage system is constituted, for example, by disk arraydevices. A disk array device is configured by arranging a multiplicityof storage devices in the form of an array and is constructed based, forexample, on RAID (Redundant Array of Independent Inexpensive Disks). Astorage device group is constituted, for example, by hard disk devicesor semiconductor memory devices and is connected by a SAN (Storage AreaNetwork) or the like. At least one logical volume (logical unit) isformed on a physical storage area provided by the storage device group,and this logical volume is provided to the host computer. The hostcomputer can conduct data writing/reading to/from the logical volume.

In the storage system, data loss is prevented and continuous operationis ensured by taking a variety of protection measures. One of them isthe utilization of a RAID configuration. For example, the possibility ofdata loss can be reduced when the disk array device employs, forexample, a redundant storage structure known as RAID 1 to RAID 6.Furthermore, duplication of physical configuration is also conducted inthe disk array system. For example, in the disk array system,multiplexing is attained by providing a plurality of main componentssuch as high-order interface circuits for conducting data communicationwith a host computer and low-order interface circuits for conductingdata communication with disk drives. Furthermore, there are alsoprovided a plurality of communication paths connecting theabove-mentioned respective main components and a plurality of powersources for supplying electric power to the main components.

Furthermore, in the disk array devices, for example, the logical volumesof the RAID structure can be duplicated and the respective identicaldata can be stored in a pair of logical volumes, primary volume andauxiliary volume.

In recent years, remote systems have been sometimes provided inlocations physically separated by a large distance from a local system,as a provision against unexpected situations such as natural disasters,this measure known as a disaster recovery. A copy of the primary volumeused in the local system is stored in the remote system. Data can betransmitted from the local system to the remote system without using ahost computer, and an auxiliary volume having the contents identical tothat of the primary volume of the local system can be created in theremote system.

Data copying is conducted in two stages to match the contents of theprimary volume and auxiliary volume. One stage is initial copying. Ininitial copying, the storage contents of the primary volume is copied inits entirety to the auxiliary volume. The other stage is differentialcopying. In differential copying, only data updated in the primaryvolume of the local system after the completion of initial copying istransferred to the auxiliary volume of the remote system. When the localsystem stops functioning due to a natural disaster or intentionalattack, the operations of the local system are continued by the remotesystem till the local system is restored. The technology for copying thestorage contents of a local disk device to an external disk devicelocated at a distance from the local disk device is known as mirroringor remote copying (Japanese Patent Application Laid-open No.H11-338646).

Remote copying can be generally classified into synchronous andasynchronous remote copying. In the case of synchronous remote copying,after the data received from the host computer has been stored in acache memory, this data is transferred to the remote system via acommunication network (SAN, IP network, or the like). If the remotesystem receives the data and stores it in a cache memory, a responsesignal indicating data reception is transmitted to the local system. Ifthe local system receives a response signal from the remote system, itposts to the host computer a write completion report notifying that thedata writing was normally conducted. Thus, in the synchronous remotecopying, the write request from the host computer and data transfer tothe remote system are executed synchronously. Therefore, because a delaycorresponding to a time period waiting for a response from the remotesystem occurs, such copying is suitable when the distance between thelocal system and remote system is comparatively short. Conversely, whenthe local system and remote system are at a large distance from eachother, the synchronous remote copying is generally unsuitable because ofthe problems associated with response delay and propagation delay.

On the other hand, in the case of asynchronous remote copying, if thelocal system receives a write request from the host computer, it storesthe received data in a cache memory and immediately sends a writecompletion report to the host computer. After sending the writecompletion report to the host computer, the local system transfers thedata to the remote system. Thus, reporting the write completion to thehost computer and transferring the data to the remote system areconducted asynchronously. Therefore, in the case of the asynchronousremote copying, the write completion report can be rapidly transmittedto the host computer, regardless of the distance between the localsystem and remote system. Therefore, the asynchronous remote copying isapplicable to the cases when the local system and remote system are at alarge distance from each other. However, in the case of an asynchronousremote copying, data transfer to the remote system has not yet beenconducted when the write completion report is sent to the host computer.Therefore, though the write completion report has been sent, it cannotbe guaranteed that the storage contents of the primary volume and thestorage contents of the auxiliary volume are matched.

Synchronization of the storage contents of the local system and remotesystem is a measure for coping with the occurrence of natural disastersand increases the reliability of the storage system. For example,considering the occurrence of large-scale natural disasters affecting awide area, such as large earthquakes, it is preferred that the localsystem and remote system be as far from each other as possible. This isbecause the shorter is the distance between the local system and theremote system, the higher is the probability that it will be impossibleto cope with wide-area failure.

On the other hand, because of physical limitations of the communicationpath between the local system and remote system, the distance betweenthe local system and remote system is naturally also limited. Forexample, when fiber channel transfer is conducted by using an opticalfiber cable, the distance at which communication is possible is aboutseveral tens of kilometers, the specific distance depending on theaperture and mode of fiber cable and the like. Therefore, when data istransmitted over a large distance by using fiber channel transfer by anoptical fiber cable, a relay system is disposed between the local systemand remote system. Introducing a relay system makes it possible toincrease, for example to double, the distance between the local systemand remote system.

Furthermore, when the copy of data is saved only in one remote system,if by any chance the data copy of the remote system is lost due to somefailure after the local system has stopped functioning, a long time willbe required to restore the storage system. Therefore, it is preferredthat the measures taken are not limited to disaster recovery and thatthe copies of the primary volume are saved in multiple locations.

If a relay system is disposed between the local system and the remotesystem, then the data of the local system can be saved in both the relaysystem and the remote system and the reliability is improved.Furthermore, because the distance between the local system and remotesystem is increased, the resistance to wide-range obstacles such aslarge earthquakes is also increased.

Further, in a storage system, as the system expands, old storage controldevices are present together with new storage control devices.Accordingly, it is desirable that the new storage control devices andold storage control devices be employed in cooperation with each other.

The present invention was created to resolve the aforesaid problems andit is an object of the present invention to provide a storage system, astorage control device, and a data relay method using the storagecontrol device that are comparatively inexpensive and can save a copy ofa volume in a plurality of locations. It is another object of thepresent invention to provide a storage system, a storage control device,and a data relay method using the storage control device that canestablish cooperation between a plurality of different storage controldevices and realize a plurality of remote copies. Other objects of thepresent invention will be evident from the description of the preferredembodiments thereof provided hereinbelow.

SUMMARY OF THE INVENTION

The storage system in accordance with the present invention, which isdesigned to resolve the aforesaid problems, is capable of transmittingthe data stored in a first storage control device to a third storagecontrol device via a second storage control device. The second storagecontrol device comprises a first virtual volume which is associated witha real volume and forms a pair with a copy source volume of the firststorage control device, a second virtual volume which is associated withthe real volume and forms a pair with a copy destination volume of thethird storage control device, a first target port having the input sidethereof connected to the copy source volume and the output side thereofconnected to the first virtual volume, a first initiator port having theinput side thereof connected to the first virtual volume, a secondtarget port having the input side thereof connected to the firstinitiator port and the output side thereof connected to the secondvirtual volume, a second initiator port having the input side thereofconnected to the second virtual volume and the output side thereofconnected to the copy destination volume, a first control program forcausing the first virtual volume to operate as an auxiliary volume ofthe copy source volume, a second control program for reflecting thestorage contents of the first virtual volume in the storage contents ofthe second virtual volume, and a third control program for causing thesecond virtual volume to operate as the primary volume of the copydestination volume, wherein the real volume is mapped to the secondvirtual volume, and the second virtual volume is mapped to the firstvirtual volume.

Examples of storage control devices include disk array devices andhighly functional fiber channel switches. Examples of host devicesinclude a variety of computer devices such as personal computer,servers, and mainframes. The first storage control device and the secondstorage control device, and the second storage control device and thethird storage control device can be bidirectionally communicablyconnected via respective communication networks. Examples ofcommunication networks include SAN, LAN (Local Area Network), speciallines, and internet. The first to third storage control devices may bedisposed in respective separate sites or may be disposed in the samesite. Alternatively, the first storage control device and the secondstorage control device can be disposed in the same site, and the thirdstorage control device can be placed in a separate site. Furthermore,the second storage control device and the third storage control devicecan be disposed in the same site, and the first storage control devicecan be disposed in a separate site.

The second storage control unit realizes two functions. One is a remotecopy relay function. The remote copy relay function is a function oftransmitting the entire data where the copy source volume of the firststorage control device is stored, or part thereof, to the third storagecontrol device via the second storage control device. Another functionis a volume copy function. The second storage control device is providedwith the first virtual volume for forming a pair with the copy sourcevolume. Therefore, the storage contents of the copy source volume issaved in two places, the first virtual volume and the copy destinationvolume, and the reliability of the storage system is increased.

The second storage control device has a first virtual volume and asecond virtual volume. Those virtual volumes are associated with thesame real volume. The first virtual volume forms a pair with the copysource volume, and the second virtual volume forms a pair with the copydestination volume. Further, the first virtual volume and the secondvirtual volume also form a pair. The volume pair as referred to hereinmeans that storage contents of corresponding volumes are matched.

The first virtual volume realizes a reception function of receiving datafrom the copy source volume by the first control program. Further, thesecond virtual volume realizes a transmission function of transmittingdata to the copy destination volume by the third control program.Synchronization of the storage contents of the first virtual volume andsecond virtual volume is conducted by the second control program. Thus,multiple virtual volumes with different control functions are formed ona single real volume. Further, the real volume is mapped to the secondvirtual volume, and the second virtual volume is mapped to the firstvirtual volume. Thus, figuratively speaking, the second virtual volumeand first virtual volume are stacked in the order of description on thereal volume.

The first virtual volume receives data from the copy source volume viathe first target port. The first virtual volume and the second virtualvolume are connected via the first initiator port and second targetport. The first initiator port and second target port are located in thesame case and are connected by a cable such as an optical fiber cable ora metal cable. The second virtual volume transmits data to the copydestination volume via the second initiator port.

Thus, data is transmitted from the first storage control device to thethird storage control device via the second storage control device.Further, the copy of the copy source volume is placed in both the secondstorage control device and the third storage control device. Copyingfrom the first storage control device to the second storage controldevice can be also called the first remote copying, and copying from thesecond storage control device to the third storage control device can bealso called the second remote copying.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the outline of the entire storagesystem of a first embodiment of the present invention;

FIG. 2 is a block diagram illustrating a schematic configuration of adisk array system that can be used in the local system, relay system,and remote system;

FIG. 3 is an explanatory drawing illustrating schematically how aplurality of virtual volumes are mapped to one real volume;

FIG. 4A shows a mapping table for mapping virtual volumes and realvolumes;

FIG. 4B is a mapping table for mapping LU and virtual volumes;

FIG. 5C is a conversion table for converting LU numbers into virtualvolume numbers;

FIG. 5B is an address conversion table for converting addresses ofvirtual volumes into addresses of real volumes;

FIG. 6 is a flow chart illustrating the outline of the entire operationof the storage system;

FIG. 7 is a block diagram illustrating the outline of the entire storagesystem of a second embodiment of the present invention;

FIG. 8 is a flow chart illustrating the outline of the entire operationof the storage system;

FIG. 9 is a block diagram illustrating the outline of the entire storagesystem of a third embodiment of the present invention;

FIG. 10 is a flow chart illustrating the outline of the entire operationof the storage system;

FIG. 11 is a block diagram illustrating the outline of the entirestorage system of a fourth embodiment of the present invention;

FIG. 12 is a block diagram illustrating the outline of the entirestorage system of a fifth embodiment of the present invention;

FIG. 13 is a block diagram illustrating the outline of the entirestorage system of a sixth embodiment of the present invention;

FIG. 14 is an explanatory drawing illustrating schematically the storagestructure of a seventh embodiment of the present invention;

FIG. 15 is an explanatory drawing illustrating schematically the storagestructure of an eighth embodiment of the present invention; and

FIG. 16 is an explanatory drawing illustrating schematically the storagestructure of a ninth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described hereinbelow basedon FIGS. 1 through 16. The present embodiments, for example, relate to astorage system in which data stored in a first storage control devicecan be transmitted to a third storage control device via a secondstorage control device, wherein the second storage control devicecomprises a first virtual volume which is associated with the realvolume and forms a pair with the copy source volume of the first storagecontrol device, a second virtual volume which is associated with thereal volume and forms a pair with the copy destination volume of thethird storage control device, a first control unit for reflecting thestorage contents of the copy source volume in the storage contents ofthe first virtual volume, a second control unit for reflecting thestorage contents of the first virtual volume in the storage contents ofthe second virtual volume, and a third control unit for reflecting thestorage contents of the second virtual volume in the storage contents ofthe copy destination volume.

The second control unit can reflect the storage contents of the firstvirtual volume in the storage contents of the second virtual volume bycopying the data stored in the first virtual volume to the secondvirtual volume via a communication path connecting an initiator port andtarget port present in the same housing.

There can be further provided a first cache memory which is associatedwith the first virtual volume for temporarily storing data that will bestored in the first virtual volume and a second cache memory which isassociated with the second virtual volume for temporarily storing datathat will be stored in the second virtual volume, and the second controlunit can reflect the storage contents of the first virtual volume in thestorage contents of the second virtual volume by copying the data storedin the first cache memory to the second cache memory.

There can be further provided a second cache memory which is associatedwith the second virtual volume for temporarily storing data that will bestored in the second virtual volume, and the second control unit canreflect the storage contents of the first virtual volume in the storagecontents of the second virtual volume by directly copying the data to bewritten to the first virtual volume to the second cache memory.

Furthermore, the present embodiments also disclose a second storagecontrol device capable of transmitting the data stored in the firststorage control device to the third storage control device, this secondstorage control device comprising a first virtual volume which isassociated with the real volume and forms a pair with the copy sourcevolume of the first storage control device, a second virtual volumewhich is associated with the real volume and forms a pair with the copydestination volume of the third storage control device, a first controlunit for reflecting the storage contents of the copy source volume inthe storage contents of the first virtual volume, a second control unitfor reflecting the storage contents of the first virtual volume in thestorage contents of the second virtual volume, and a third control unitfor reflecting the storage contents of the second virtual volume in thestorage contents of the copy destination volume.

Here, the real volume can be mapped to the second virtual volume, andthe second virtual volume can be mapped to the first virtual volume.

Further, the first virtual volume and second virtual volume can beindependently associated with the real volume.

The second control unit can reflect the storage contents of the firstvirtual volume in the storage contents of the second virtual volume bycopying the data stored in the first virtual volume to the secondvirtual volume via a communication path connecting the initiator portand target port located in the same housing.

The real volume may be present outside the second storage controldevice. Thus, the external real volume can be effectively used bymapping the real volume of a separate storage control device locatedoutside to the second virtual volume.

Here, at least either the first virtual volume or second virtual volumescan be provided in a pluality.

For example, a plurality of second virtual volumes can be provided andeach second virtual volume can respectively form a pair with differentcopy destination volumes. Alternatively, a plurality of first virtualvolumes can be provided and each first virtual volume can respectivelyform a pair with different copy source volumes. In this case, forexample, one real volume may be prepared for each system of remotecopying.

The first control unit, second control unit, and third control unit canbe mounted on respective channel adapters for controlling datacommunication with a host device.

Further in the present preferred embodiment, there is also disclosed adata relay method using a storage control device for transmitting thedata stored in a first storage control device to a third storage controldevice via a second storage control device. This data relay methodcomprises the steps of setting a first virtual volume and a secondvirtual volume, each being associated with a real volume, into thesecond storage control device, forming a first pair from the firstvirtual volume and the copy source volume of the first storage controldevice, forming a second pair from the second virtual volume and thecopy destination volume of the third storage control device,synchronizing the storage contents of the copy source volume and thefirst virtual volume, synchronizing the storage contents of the firstvirtual volume and the second virtual volume, and synchronizing thestorage contents of the second virtual volume and the copy destinationvolume.

First Embodiment

The first embodiment will be described below based on FIGS. 1 through 6.FIG. 1 is a block diagram illustrating the outline of the storagesystem. The present storage system, as will be described hereinbelow,comprises a host computer 1, a local system 10 serving as a firststorage control device, a relay system 20 serving as a second storagecontrol device, a remote system 30 serving as a third storage controldevice, and another storage control device 40.

The host computer 1 is a computer device comprising informationprocessing resources such as a CPU (Central Processing Unit) or amemory, and is constituted, for example, by a personal computer, aworkstation, a server, a mainframe, or the like. The host computer 1comprises an information input device (not shown in the figures) such asa keyboard switch, a pointing device, a microphone, or the like, and aninformation output device (not shown in the figures) such as a monitordisplay, a speaker, or the like. Furthermore, the host computer 1 isalso provided with an application program (not shown in the figures)such as a database software for using a storage area provided by thelocal system 10, and an adapter (not shown in the figures) for accessingthe local system 10 via a communication network CN1.

The host computer 1 is connected to the local system 10 via thecommunication network CN1. For example, a SAN can be used as thecommunication network CN1. However, a LAN is not always necessarilyused, and internet, or a special circuit may be also used. When a SAN isused, the transmission can be conducted in block units following thefiber channel protocol. When a LAN is used, the transmission can beconducted in file units following the TCP/IP (Transmission ControlProtocol/Internet Protocol). When internet is used, for example, acommand set of SCSI (Small Computer System Interface) can be serializedas TCP/IP packets. Alternatively, there is also a method fortransmitting according to the TCP/IP by capsuling the fiber channelframe. Note that although the host computer 1 shown in the figure isconnected only to the local system 10, such a configuration is notalways necessary and the host computer 1 may be also connected to therelay system 20 and remote system 30.

The local system 10 is configured, for example, as a disk arraysubsystem. The local system 10 can use a copy source volume V11. Thecopy source volume V11 can be configured as a logical unit or logicalvolume and can be recognized from the host computer 1. A LUN (LogicalUnit Number) is allocated to the copy source volume V11. The copy sourcevolume V11 can be virtually provided on the real volume (not shown inthe figure) in the local system 10. Alternatively, the copy sourcevolume V11 can be also formed by mapping the real volume (not shown inthe figures) located outside the local system 10 to an intermediatestorage hierarchy (also called a VDEV).

The local system 10 receives commands from the host computer 1 via atarget port T11. Further, the local system 10 transmits commands to theremote system 30 via an initiator port IP11. The term “initiator” heremeans the control side, and the term “target” means the controlled side.Commands for controlling separate devices are transmitted from theinitiator port, and the commands from the host device are inputted intothe target port. The host computer 1 can read the data stored in thecopy source volume V11 or write the data by transmitting a read commandor a write command to the local system 10. If the copy source volume V11is updated, a write command is transmitted from the IP11 to the relaysystem 20. If the relay system 20 receives a write command from thelocal system 10, it updates the internal virtual volume V21 and alsotransmits a write command to the remote system 30. As a result, thevolume having the storage contents identical to the storage-contents ofthe copy source volume V11 is formed in the relay system 20 and remotesystem 30.

The relay system 20 is configured, for example, as a disk arraysubsystem. The relay system 20 comprises a first virtual volume V12 anda second virtual volume V21 associated with the same real volume R1. Thereal volume R1 is provided inside a separate storage control device 40located outside the relay system 20. Further, as will be describedbelow, the real volume R1 can be also provided inside the relay system20. Furthermore, the relay system 20 also comprises a first cache memoryC12 and a second cache memory C21. The first cache memory C12 isassociated with the first virtual volume V12 and stores temporarily thedata for the first virtual volume V12. The second cache memory C21 isassociated with the second virtual volume V21 and stores temporarily thedata for the second virtual volume V21.

The first virtual volume V12 forms a pair with the copy source volumeV11 of the local system 10. In other words, a first remote copy pair isformed for which the copy source volume V11 is considered as a primaryvolume and the first virtual volume V12 is considered as an auxiliaryvolume. The second virtual volume V21 forms a pair with the copydestination volume V22 of the remote system 30. In other words, a secondremote copy pair is formed for which the second virtual volume V21 isconsidered as a primary volume and the copy destination volume V22 isconsidered as an auxiliary volume. Thus, as described below, the storagecontents of the respective virtual volumes V12 and V22 are also made tosynchronize with each other. Further, as will be described hereinbelow,the second virtual volume V21 can be recognized from the outside bybeing associated with (by mapping to) a virtual real volume R2. Further,the first virtual volume V12 can be recognized from the outside by beingassociated with a logical unit (not shown in the figures).

On the other hand, focusing attention on the configuration of thecommunication path, a first target port TP21 is connected to theinitiator port IP11 of the local system 10 via a communication networkCN2. The output side of the first target port TP21 is connected to thefirst virtual volume V12. The communication network CN2 is constituted,for example, by a SAN. A command from the local system 10 is received bythe first target port TP21 from the initiator port IP11 via thecommunication network CN1.

A first initiator port IP21 is connected by the input side thereof tothe first virtual volume V12 and by the output side thereof to a secondtarget port TP22 via a communication network CN3. The communicationnetwork CN3 is constituted, for example, by a SAN. A cable constitutingthe communication network CN3 is, for example, arranged to pass theoutside of the relay system 20. A message transmitted from the firstvirtual volume V12 to the second virtual volume V21 is received by thesecond target port TP22 from the first initiator port IP21 via thecommunication network CN3.

The output side of the second target port TP22 is connected to thesecond virtual volume V21. The second initiator port IP22 is connectedby the input side thereof to the second virtual volume V21 and by theoutput side thereof to a target port TP31 of the remote system 30 via acommunication network CN4. The communication network CN4 is constituted,for example, by a SAN or internet. A command from the second virtualvolume V21 is received by the target port TP31 of the remote system 30from the initiator port IP22 via the communication network CN4.

The remote system 30 is configured, for example, as a disk arraysubsystem. The remote system 30 can use a copy destination volume V22.The copy destination volume 22 is configured as a logical unit orlogical volume and is a logical storage device that can be recognizedfrom another device (relay system 20 or the like). A LUN is allocated tothe copy destination volume V22. The copy destination volume V22 forms apair with the second virtual volume V21. The copy destination volume V22can be virtually provided on a real volume (not shown in the figures) inthe remote system 30. Alternatively, the copy destination volume V22 canbe also formed by mapping the real volume (not shown in the figure)located outside of the remote system 30 to an intermediate storagehierarchy. If the remote system 30 receives a write command from therelay system 20 via the target port TP31, it writes and updates data inthe copy destination volume V22.

The other storage control device 40 is used for providing a real volumeR1 to the relay system 20. In other words, the storage control device 40is used as a provision source of physical storage areas. A target portTP41 of the storage control device 40 is connected to the initiator portIP22 of the relay system 20 via a communication network CN5. Thecommunication network CN5 is constituted, for example by a SAN. The realvolume R1 is mapped to the second virtual volume V21, and the secondvirtual volume V21 is mapped to the second real volume R2, this mappingbeing described hereinbelow in greater detail. The second real volume R2is mapped to the first virtual volume V12.

Here, the second real volume R2 is a virtual entity and has no physicalentity. The second real volume R2 has the second virtual volume V21mapped thereto and is linked to the first real volume R1 via the secondvirtual volume V21. Therefore, the entity of the second real volume R2is the first real volume R1.

FIG. 2 is a block diagram illustrating an example of the disk arraysubsystem. The disk array subsystem shown in FIG. 2 can be used in thelocal system 10, relay system 20, and remote system 30.

The disk array subsystem 100 can be connected to the reception externaldevice (host device) 200 via a communication network CN11. Furthermore,the disk array subsystem 100 can be connected to a transmission externaldevice (external device) 300 via a communication network CN12. When thedisk array subsystem 100 is employed in the local system 10, the hostdevice 200 corresponds to the host computer 1, and the external device300 corresponds to the relay system 20. Furthermore, when the disk arraysubsystem 100 is employed in the relay system 20, the host device 200corresponds to the local system 10, and the external device 300corresponds to the remote system 30. Further, when the disk arraysubsystem 100 is employed in the relay system 20, it is not necessary toprovide a local storage device 150. This is because mapping a storagedevice contained in the external storage control device to an internalLU (or mapping to an intermediate storage hierarchy) located below theLU makes it possible to use it as an own storage device.

The disk array subsystem 100 can be generally divided into a controlsection and a storage section. The control section is composed, as willbe described hereinbelow, of a channel adapter (abbreviated hereinbelowas CHA) 110, a cache package 120, and a disk adapter (abbreviatedhereinbelow as DKA) 130. The storage section is composed of a storagedevice 150.

The disk array subsystem 100 can comprise a plurality of CHA110. EachCHA110 conducts data communication with the host device 200. Each CHA110comprises ports (indicated as TP (target port) and IP (initiator port))for conducting communication with external devices. Furthermore, eachCHA110 comprises a plurality of processors 111 or local memories (notshown in the figures). A network address such as WWN (World Wide Name)or IP address is allocated to each CHA110. The command received via thetarget port is interpreted by the processor 111. The command is storedfrom the processor to the shared memory 121 via the command adapter (notshown in the figures). The data received from the host device 200 isstored in the cache memory 122 via the data adapter (not shown in thefigures).

The disk array subsystem 100 can comprise a plurality of cache packages120. Each cache package is configured, for example, as a printed boardand comprises a shared memory 121 and a cache memory 122. Managementinformation such as RAID group configuration information and controlinformation such as commands are stored in the shared memory 121.Furthermore, tables T1 through T4 as described below can be also storedin the shared memory 121. Data received from the host device 200 anddata read out from the storage device 150 are stored in the cache memory122. Each CHA110 and each cache package 120 are connected via a switch141. Thus, each CHA110 can access all the cache packages 120.

The disk array subsystem 100 can comprise a plurality of DKA130. EachDKA130 conducts data communication with the storage device 150. EachDKA130 is configured by providing respective processors or localmemories (neither is shown in the figures) and connected to each storagedevice 150 via ports (not shown in the figures). Each DKA130 and cachepackages 120 are connected via switches 141, and each DKA130 can accessall the cache packages 120. Each DKA130 monitors as to whether a commandfrom an external device has been received by periodically referring tothe shared memory 121. For example, in the case of a read command, theDKA130 reads data by accessing the storage device 150 that stores therequested data. The DKA130 converts the physical address into a logicaladdress (LBA: Logical Block Address) and stores the read-out data in thecache memory 122. In the case of a write command, the DKA130 acquiresfrom the cache memory 122 the data that are requested to be written,conduct address conversion and the like, and writes the data to thedesignated address.

Each storage device 150 is connected to each DKA130 via a communicationcable 142. One RAID group can be composed of a prescribed number (forexample, four) of storage devices 150. At least one logical volume whichis a logical storage area is formed in the physical storage areaprovided by each storage device 150 of each RAID group.

The external device 300 can have a configuration identical to that ofthe disk array subsystem 100 and comprises a storage device 350.

FIG. 3 is an explanatory drawing illustrating schematically the relationbetween the volumes. The real volume R is mapped to the second virtualvolume V21, and the second virtual volume V21 is mapped to the secondreal volume R2. Mapping means that the address of a certain volume isallocated to the address of another volume. More specifically, mappingis possible, for example, by mapping the address of the second realvolume R2, the address of the virtual volume V21, and the address of thereal volume R. When the address of the second real volume R2 has beendesignated, if the address for this R2 is converted into the address forV21, and the address for V21 is converted into the address for R, thedata stored in the real volume R can be read or the data can be writteninto the real volume R. More specifically, information other than theaddress information, for example, such as WWN, LU number, and-volumesize is also catalogued in the mapping table for mapping the volumes.The “LU” shown in FIG. 3 is a volume provided with a LUN and isrecognized from the external device (host computer or other storagecontrol unit). Therefore, the IP21 of the relay system 20 can recognizethe second real volume R2 and transmit a command. However, as describedhereinabove, an independent entity such as the second real volume R2 isnot actually present, and this entity is the first real volume R1.

The second real volume R2 is further mapped to the first virtual volumeV12, and the first virtual volume V12 is mapped to the LU. As a result,the initiator port IP11 of the local system 10 can recognize the firstvirtual volume V12 and can transmit a command. In FIG. 3, the virtualvolume V21 is mapped to one real volume R, but such a mapping is notlimiting and, for example, one virtual volume V21 may be formed from aplurality of real volumes.

FIG. 4 is an explanatory drawing illustrating the schematicconfiguration of the mapping table for mapping the volumes of two types.FIG. 4 and FIG. 5 show generalized configurations of the tables andtherefore those configurations do not necessarily correspond to theconfigurations shown in FIG. 1 and FIG. 3. FIG. 4(a) shows a virtualvolume—real volume mapping table (referred to hereinbelow as a V/Rtable) Ti for mapping the virtual volumes and real volumes, and FIG.4(b) shows a LU—virtual volume mapping table (referred to hereinbelow asa LU/V table) T2 for mapping the LU and the virtual volumes.

First, the V/R table T1 will be explained. The V/R table T1, as shown inFIG. 4(a), maps to each other the start address of the allocated realvolumes, the size of virtual volumes, and the multiple virtualizationdecision information for each virtual volume number (#V). The multiplevirtualization decision information is the information for deciding asto whether a plurality of virtual volumes have been allocated to onereal volume. FIG. 4(a) shows a configuration in which a plurality ofvirtual volumes can be mapped to one real volume. When a virtual volumeis mapped to a plurality of real volumes, managing may be conducted byalso including the real volume number. Referring to the V/R table T1makes it possible to decide to which range in the real volume a certainvirtual volume is allocated.

The LU/V table T2, as shown in FIG. 4(b), maps to each other the numberof the allocated virtual volume, the start address in the virtualvolume, and the size of virtual volumes for each LU number (#LU). FIG.4(b) shows a configuration in which a plurality of LU can be set for aplurality of virtual volumes. Referring to the LU/V table T2 makes itpossible to decide to which LU is allocated to which range of all thevirtual volumes.

FIG. 5(a) is a volume number conversion table T3 for the LU number andvirtual volume number. The volume number conversion table maps andmanages the LU number and virtual volume number. The conversion table T3corresponds to the LU/V table T2 and will be referred to in thebelow-described processing operation of the present embodiment.

FIG. 5(b) is an address conversion table T4 for conducting addressconversion of virtual volumes and real volumes. The address conversiontable T4 maps and manages the WWN and LU number of corresponding realvolumes (path information), start address (start LBA: Logic BlockAddress) and final address (MaxLBA), and volume attribute. This addressconversion table T4 corresponds to the V/R table T1 and will be referredto in the below-described processing operation of the presentembodiment. The above-described tables T1 through T4 can be stored inthe shared memory 121.

FIG. 6 is a flow chart illustrating the outline of the entire operationof the storage system. In this flow chart, a mode is shown in which whendata update is conducted from the host computer 1 to the copy sourcevolume V11 of the local system 10, this data update is reflected in theremove system 30 via the relay system 20.

The storage system reflects the data update from the host computer 1 inthe local system 10, relay system 20, and remote system 30. Thus, in thestorage system, copies of the copy source volume V11 used by the hostcomputer 1 are generated in both the relay system 20 and the remotesystem 30.

The flow chart shown in FIG. 6 is mainly executed by the CHA110 of eachsystem. More specifically, it is executed by the CHA110 having aninitiator port (IP) or target port (TP) relating to this processing.Partial processing is executed by the DKA130 of each system.

First, all the storage contents of the copy source volume V11 of thelocal system 10 are copied into both the real volume R of the relaysystem 20 and the copy destination volume V22 of the remote system 30.This copying is called the initial copying. The initial copyingsynchronizes the contents of the volume systems V11, R, V22.

If the host computer 1 conducts data update (issues a write command)with respect to the copy source volume V11 in this state, theinformation contents of the copy source volume V11 is updated inresponse to this command. Therefore, a difference occurs with thestorage contents after the initial copying. Referring to an example ofthe local system 10 having the configuration shown in FIG. 2, when awrite command has been issued by the host computer 1, the CHA110 storesthe update data in the cache memory 122 and stores the record that thewrite command has been received in the shared memory 121. If the DKA130detects the presence of the write command by referring to the sharedmemory 121, it reads the update data stored in the cache memory 122 andstores it in a prescribed storage area of the storage device 150.

The local system 10 transmits the write command from the initiator portIP 11 to the relay system 20 via the communication network CN2 inparallel with the update of the copy source volume V11 or after theupdate of the copy source volume V11 has been completed (S1). This writecommand is composed of the update data which is to be stored and theinformation designating the storage address, for example, as[WWN#/LU#/LBA# . . . ].

The relay system 20 received the write command from the local system 10via the target port TP21 (S11). The TP21 converts the LU number (LU#)present in the write command into the virtual volume number (V#) byreferring to the volume number conversion table T3 (S12). Then, the TP21conduct data reception processing as the first virtual volume V12 (S13)and stores the received data in the first cache memory C12 (S14). TheTP21 conducts address conversion of the data stored in the cache memoryC12 by referring to the address conversion table T4 (S15). The addressof update data is thus converted to the address corresponding to thesecond real volume R2. After the address conversion, the TP21 issues amessage (MSG) to the IP21.

This message is an internal indication for writing data into the secondreal volume R2. However, as described hereinabove, because the secondreal volume R2 is a virtual eneity, data are not actually written intothe second real volume R2. The IP21 that has received the message issuesa write command to the TP22 (S22). Thus, The write request from thefirst virtual volume V12 to the second real volume R2 is converted intothe write request into the second virtual volume V21. Data inputted intothe first virtual volume V12 is transferred into the second virtualvolume V21 via the communication network CN3.

If the TP22 receives the write command from the IP21 (S31), it conductsdata reception processing as the second virtual volume V21 (S32) andwrites the received data into the second cache memory C21 (S33). TheTP22 converts the LU numbers to the virtual volume numbers (V21 numbers)(S34) by referring to the volume number conversion table T3 and issues amessage to the IP22 (S35).

If the IP22 receives the message from the TP22 (S41), it conductstransmission processing as the main volume (V21) of the copy destinationvolume V22 (S42). The IP22 converts the address setting the virtualvolume V21 as the object into the address for the copy destinationvolume V22 by referring to the address conversion table T4 (S43). Then,the IP22 transmits a write command to the remote station 30 via thecommunication network CN4 (S44).

If the TP31 of the remote system 30 receives the write command from therelay system 20, it writes the received data into the copy destinationvolume V22 (this is not shown in the figures). Further, the IP22 of therelay system 20 transmits a write command to the real volume R of theother storage control unit 40 via the communication network CN5 (this isnot shown in the figures). If the other storage control unit 40 receivesthe write command from the relay system 20, it writes the received datain the real volume R1.

Here, data writing from the local system 10 to the relay system 20 isconducted in a synchronous mode. Thus, if a write command is transmittedfrom the local system 10 to the relay system 20, the relay system 20stores the received data in the cache memory C12 and returns a writecompletion report to the local system 10. If the local system 10receives the write completion report from the relay system 20, itreports the write completion to the host computer 1.

On the other hand, data writing from the relay system 20 into the remotesystem 30 and data writing from the relay system 20 to the real volumeR1 are conducted in asynchronous modes. That is, writing is completedonce the data has been stored in the second cache memory C21 (cachememory for transmission) of the relay system 20, and then datatransmission to the copy destination volume V22 is conducted.

In the present embodiment, as an example, a comparatively short distancewas set between the local system 10 and the relay system 20, and acomparatively large distance was set between the relay system 20 and theremote system 30. Therefore, the synchronous mode was used for datatransfer between the local system 10 and the relay system 20, and theasynchronous mode was used for data transfer between the relay system 20and the remote system 30.

In the present embodiment, as described hereinabove, a plurality ofvirtual volumes V12, V21 are mapped to one real volume R1, one virtualvolume V12 is used for data reception, and the other virtual volume V21is used for data transmission. Therefore, the size of real volume can bedecreased by half and the cost can be reduced by comparison with thecase in which individual real volumes are prepared for each ofrespective virtual volumes V12, V21. Thus, multiple control can beexecuted at a low cost because a plurality of virtual volumes V12, V21with different control objects can be allocated to one real volume R1.The virtual volume other than the virtual volume for executing the relayfunction of remote copying can be also mapped to the shared real volumeand the control function for other services can be allocated to thisvirtual volume.

Further, the reliability of the storage system can be increased becausea copy of the copy source volume V11 can be placed in both the relaysystem 20 and the remote system 30.

Furthermore, because the real volume R1 of the other storage controlunit 40 is used by allocating to each virtual volume V12, V21 of therelay system 20, the already present volume R1 can be used as if it isan internal volume of the relay system 20. Therefore, the relay system20 can be configured by reusing the already present volume R1 and theconventional storage resources can be used effectively. For example,when the relay system 20 is a high-capacity system, for example, suchthat has a large loading amount of the cache memory and a high dataprocessing capacity, even when the other storage control unit 40 has alow capacity, this low capacity of the other storage control unit 40 canbe concealed and the real volume R1 can be used. Further, the effect ofthe above-described embodiments places no limitation on the scope of thepresent invention; the same is true for the below-described otherembodiments.

Second Embodiment

The second embodiment will be explained with reference to FIG. 7 andFIG. 8. This embodiment is equivalent to a modification example of thefirst embodiment. A specific feature of this embodiment is that datatransfer from the first virtual volume V12 to the second virtual volumeV21 is realized by interchache copying.

FIG. 7 is a block diagram illustrating the outline of the storage systemof the present embodiment. In the present embodiment, the communicationnetwork CN3 for connecting the IP21 and TP22 is not provided. A linkbetween the virtual volumes V12, V21 is realized by communication usinga shared memory or local memory. Thus, communication between the volumesV12, V21 is conducted via the shared memory 121 shown in FIG. 2 or alocal memory present in each CHA110. Therefore, in the presentembodiment, a cable for connecting the IP21 and TP22 becomes unnecessaryand the mechanical structure can be simplified.

FIG. 8 is a flow chart illustrating the outline of the entire operationof the present embodiment. Because the operation of the presentembodiment is mostly identical to that described in the firstembodiment, the explanation will be focused on the configuration whichis specific to the present embodiment to avoid redundant explanation.

If the TP 21 of the relay system 20 receives a write command from thelocal system 10 (S11), the conversion of volume number is conducted(S12, S13) and the received data is stored in the first cache memory C12(S14). The data stored in the first cache memory C12 is copied into thesecond cache memory C21. Further, the. TP21 converts the addressdesignated by the write command into the address for the second virtualvolume V21 (S15 a) by referring to the address conversion table-T4 andissues a message to the IP 22 (S16). This message is posted via theshared memory or local memory.

If the IP 22 receives the message from the TP21 (S51), it starts thedata reception processing as the second virtual volume V21 (S52).However, as described hereinabove, the reception data stored in thefirst cache memory C12 has already been copied into the second cachememory C21 by intercache copying. Therefore, in the present embodiment,the processing of steps S52, S53 is a formal processing. Then, similarlyto the first embodiment, the reception data copied into the second cachememory C21 is transferred from the IP22 to the copy destination volumeV22 via the communication network CN4 (S56). Further, the reception datacopied into the second cache memory C21 is transferred to the realvolume R via the communication network CN5.

Third Embodiment

The third embodiment will be explained hereinbelow based on FIG. 9 andFIG. 10. This embodiment corresponds to the second modification exampleof the first embodiment. A specific feature of the present embodiment,as compared to the second embodiment is that a single cache memory C21can be shared for use between a plurality of virtual volumes V12, V21.

FIG. 9 is a block diagram illustrating the outline of the storage systemof the present embodiment. In this embodiment, too, similarly to thesecond embodiment, the communication network CN3 connecting the IP21 andTP22 is not provided. A link between the virtual volumes V12, V21 isrealized by communication using a shared memory or local memory.Furthermore, in the present embodiment, only the cache memory C21 isprovided. Therefore, in the present embodiment, a cable connecting theIP21 and TP22 is not required and half of the cache memory will suffice.Therefore, the mechanical structure can be further simplified.

FIG. 10 is a flow chart illustrating the outline of the entire operationof the present embodiment. Because the operation of the presentembodiment, similarly to that of the second embodiment, is mostlyidentical to that described in the first embodiment, the explanationwill be focused on the configuration which is specific to the presentembodiment to avoid redundant explanation.

If the TP21 present in the relay system 20 receives a write command fromthe local system 10 (S11), the conversion of volume number is conducted(S12, S13). The TP21 directly writes the data received from the localsystem 10 to the cache memory C21 (S14 a). Then, the TP21 converts theaddress designated by the write command to the address for the secondvirtual volume V21 (S15 a), and issues a message to the IP22 (S16). Themessage posting is conducted via the shared memory or local memory.

If the IP22 receives the message from the TP21 (S51), it starts the datareception processing as a second virtual volume V21 (S52). As describedhereinabove, the data received by the first virtual volume V12 hasalready been stored in the cache memory C21. Accordingly, the IP22 doestnot conduct data storing into the cache memory C21 (in the presentembodiment, S53 is unnecessary and therefore omitted) and starstransmission processing as primary volume (S54-S56).

Fourth Embodiment

The fourth embodiment will be explained based on FIG. 11. Thisembodiment corresponds to the third modification example of the firstembodiment. FIG. 11 is a block diagram illustrating the outline of theentire storage system. A specific feature of the present embodiment, ascompared to the second embodiment, is that a plurality of virtualvolumes V12, V21 with different control contents are allocated to aninternal real volume R1 a.

Fifth Embodiment

FIG. 12 is a block diagram illustrating the outline of the entirestorage system of fifth embodiment. This embodiment corresponds to thefourth modification example of the first embodiment. A specific featureof the present embodiment is that a plurality of virtual volumes fortransmission are provided and data are transmitted to respectivedifferent remote sites. The case is considered in which the presentembodiment is applied to the configuration of the second modificationexample (third embodiment), but similar applications are also possibleto other above-described embodiments.

In the relay system 20 of the present embodiment, one first virtualvolume V12 for reception control and two second virtual volumes V21 a,V21 b for transmission control are provided. Each of the second virtualvolumes V21 a, V21 b is mapped to respective identical real volume R1.Therefore, in the present embodiment, three virtual volumes V12, V21 a,V21 b are allocated to one real volume R1. Further, the connection fromthe first virtual volume V12 to each second virtual volume V21 a, V21 bis conducted by communication via a shared memory or local memory.

If the first virtual volume V12 receives a write command from the localsystem 10, the reception data is written into the shared cache memoryC21. This cache memory C21 is referred to by each of the second virtualvolumes V21 a, V21 b.

One second virtual volume V21 a is connected to a copy destinationvolume V22 a of a first remote system 30 a from the IP22 via acommunication network CN4 a. This, virtual volume V21 a forms a pairwith the copy destination volume V22 a and becomes a primary volumecorresponding to the copy destination volume V22 a. Similarly, the othersecond virtual volume V21 b is connected to a copy destination volumeV22 b of the second remote system 30 b from the IP23 via a communicationnetwork CN4 b. The virtual volume V21 b is used as a primary volume ofthe copy destination volume V22 b.

The data received from the local system 10 is written into the sharedcache memory C21. Each of the second virtual volumes V21 a, V21 basynchronously transfers the data to the copy destination volumes V22 a,V22 b forming respective pairs. Furthermore, any one of the secondvirtual volumes V21 a, V21 b asynchronously transfers the data to thereal volume R1.

With the present embodiment, copies of the copy source volume V11 can beplaced into a plurality of remote systems 30 a, 30 b and reliability canbe further increased. Furthermore, because three virtual volumes V12,V21 a, V21 b are allocated to one real volume R1, remote copying tomultiple locations can be implemented at a lower cost.

Sixth embodiment

FIG. 13 is a block diagram illustrating the outline of the entirestorage system of the sixth embodiment. This embodiment corresponds tothe fifth modification example of the first embodiment. A specificfeature of the present embodiment is that the same port can be used asthe target port TP21 at one time and as the initiator port IP21 atanother time.

Data copying from the copy source volume V11 of the local system 10 tothe first virtual volume V12 and data copying from the first virtualvolume V12 to the second virtual volume V21 are conducted in respectivedifferent intervals, that is, exclusively. Therefore, the same portfunctions as the initiator port TP21 during data copying from the copysource volume V11 to the first virtual volume V12 and functions as theinitiator port IP21 during data copying from the first virtual volumeV12 to the second virtual volume V21.

This port TP21/IP21 is connected via a change-over switch to the localsystem 10 and remote system 30, respectively. When a write command isreceived from the local system 10, the port TP21/IP21 is connected viathe switch 50 to the local system 10. When a write command istransmitted to the remote system 30, the port TP21/IP21 is connected viathe switch 50 to the remote system 30.

Further, this signal port TP21/IP21 can be divided into the TP21 andIP21 to obtain a configuration in which each port can operate as asingle port. In this case, the changeover switch 50 becomes unnecessary.

Seventh Embodiment

The seventh embodiment will be explained based on FIG. 14. Thisembodiment corresponds to the sixth modification example of the firstembodiment. In this embodiment, a lower-order virtual volume V100 isallocated to the real volume R100. Further, multiple LU101-103 areallocated to the lower-order virtual volume V100. Furthermore, among theLU101-103, the upper virtual volume V200 is allocated to one LU102, andthe LU200 is allocated to this upper-order virtual volume V200.

Comparison with the configuration of the first embodiment, shows thatthe real volume R100 corresponds to the real volume R1, the lower-ordervirtual volume V100 corresponds to the second virtual volume V21, andthe upper-order virtual volume V200 corresponds to the first virtualvolume V12. Therefore, the relay system 20 uses a storage structurecomposed of the LU200, V200, LU102, part of V100, and part of R100.

Other LU101, 103 can be used for the same or different respectiveservices. For example, the LU101 and LU103 can be connected torespective other host computers, and the remote copying of the copysource volume V11 can be used as a different service (customermanagement, mail server, and the like).

Eighth embodiment

The eighth embodiment will be explained based on FIG. 15. Thisembodiment corresponds to the seventh modification example of the firstembodiment. This embodiment can be advantageously used in the secondembodiment (or third embodiment).

The respective different virtual volumes V100, V101 are mapped in aparallel relationship to a single real volume R100. Further, a pluralityof respective LU are set for the virtual volumes V100, V101. A total ofthree LU, namely, LU101-103, are set in a parallel relationship for onevirtual volume V100, and the three LU, namely, LU104-106, are set in aparallel relationship for the other virtual volume V101. Here, thecorresponding LU of the two groups are allocated to the same storagearea. That is, LU101 and LU104, LU102 and LU105, and LU103 and LU106form respective pairs and share part of the storage area of the realvolume R100.

Comparison with the configuration of the second embodiment shows thatthe real volume R100 corresponds to the real volume R1, for example, theLU101 corresponds to the LU of the first virtual volume V1, and theLU104 corresponds to the LU of the second virtual volume V21. Further, apair of different LU (LU102 and LU105, and the like) may be also used.Pairs of remaining LU can be used for respective separate applications(services).

Ninth Embodiment

The ninth embodiment will be explained based on FIG. 16. This embodimentcorresponds to the eighth modification example of the first embodiment.This embodiment can be especially advantageously used in the thirdembodiment.

A virtual volume V100 is allocated to the real volume R100, and each ofthe two LU101, 102 is allocated to part of the virtual volume V100.Comparison with the third embodiment shows that the real volume R100corresponds to the real volume R1, the LU101 corresponds to the LU ofthe first virtual volume V12, and the LU102 corresponds to he LU of thesecond virtual volume V21.

Furthermore, a portion of the virtual volume V100, which is shared bythe LU101, 102 can be also considered as a shared cache memory C21.Thus, it can be assumed that LU101, 102 are created in the storage spaceof the cache memory C21.

Further, the present invention is not limited to the above-describedembodiments. Various modifications and changes that will be apparent tothose skilled in the art may be resorted to, without departing from thescope of the invention. For example, remote copying of the local system10 and relay system 20 may be also conducted in an asynchronous mode.Further, the present invention is not limited to the application to theso-called open system, and the application to a mainframe is alsopossible.

1. A storage system capable of transmitting data stored in a firststorage control device to a third storage control device via a secondstorage control device, wherein said second storage control devicecomprises: a first virtual volume which is associated with a real volumeand forms a pair with a copy source volume of said first storage controldevice; a second virtual volume which is associated with said realvolume and forms a pair with a copy destination volume of said thirdstorage control device; a first target port having the input sidethereof connected to said copy source volume and the output side thereofconnected to said first virtual volume; a first initiator port havingthe input side thereof connected to said first virtual volume; a secondtarget port having the input side thereof connected to said firstinitiator port and the output side thereof connected to said secondvirtual volume; a second initiator port having the input side thereofconnected to said second virtual volume and the output side thereofconnected to said copy destination volume; a first control program forcausing said first virtual volume to operate as an auxiliary volume ofsaid copy source volume; a second control program for reflecting storagecontents of said first virtual volume in storage contents of said secondvirtual volume; and a third control program for causing said secondvirtual volume to operate as the primary volume of said copy destinationvolume, and wherein said real volume is mapped to said second virtualvolume, and said second virtual volume is mapped to said first virtualvolume.
 2. A storage system capable of transmitting data stored in afirst storage control device to a third storage control device via asecond storage control device, wherein said second storage controldevice comprises: a first virtual volume which is associated with a realvolume and forms a pair with a copy source volume of said first storagecontrol device; a second virtual volume which is associated with saidreal volume and forms a pair with a copy destination volume of saidthird storage control device; a first control unit for reflectingstorage contents of said copy source volume in storage contents of saidfirst virtual volume; a second control unit for reflecting storagecontents of said first virtual volume in storage contents of said secondvirtual volume; and a third control unit for reflecting storage contentsof said second virtual volume in storage contents of said copydestination volume.
 3. The control system according to claim 2, whereinsaid second control unit reflects storage contents of said first virtualvolume in storage contents of said second virtual volume by copying datastored in said first virtual volume to said second virtual volume via acommunication path connecting an initiator port and a target portlocated in the same housing.
 4. The control system according to claim 2,further comprising a first cache memory which is associated with saidfirst virtual volume for temporarily storing data to be stored in saidfirst virtual volume, and a second cache memory which is associated withsaid second virtual volume for temporarily storing data to be stored insaid second virtual volume, wherein said second control unit reflectsstorage contents of said first virtual volume in storage contents ofsaid second virtual volume by copying the data stored in said firstcache memory to said second cache memory.
 5. The control systemaccording to claim 2, further comprising a second cache memory which isassociated with said second virtual volume for temporarily storing datato be stored in said second virtual volume, wherein said second controlunit reflects storage contents of said first virtual volume in storagecontents of said second virtual volume by directly copying data writtenin said first virtual volume to said second cache memory.
 6. A secondstorage control device capable of transmitting data stored in a firststorage control device to a third storage control device, said secondstorage control device comprising: a first virtual volume which isassociated with a real volume and forms a pair with a copy source volumeof said first storage control device; a second virtual volume which isassociated with said real volume and forms a pair with a copydestination volume of said third storage control device; a first controlunit for reflecting the storage contents of said copy source volume instorage contents of said first virtual volume; a second control unit forreflecting storage contents of said first virtual volume in storagecontents of said second virtual volume; and a third control unit forreflecting storage contents of said second virtual volume in storagecontents of said copy destination volume.
 7. The second storage controldevice according to claim 6, wherein said real volume is mapped to saidsecond virtual volume, and said second virtual volume is mapped to saidfirst virtual volume.
 8. The second storage control device according toclaim 6, wherein said first virtual volume and said second virtualvolume are independently associated with said real volume.
 9. The secondstorage control device according to claim 6, wherein said second controlunit reflects storage contents of said first virtual volume in storagecontents of said second virtual volume by copying data stored in saidfirst virtual volume to said second virtual volume via a communicationpath connecting an initiator port and a target port located in the samehousing.
 10. The second storage control device according to claim 6,further comprising a first cache memory which is associated with saidfirst virtual volume for temporarily storing data to be stored in saidfirst virtual volume, and a second cache memory which is associated withsaid second virtual volume for temporarily storing data to be stored insaid second virtual volume, wherein said second control unit reflectsstorage contents of said first virtual volume in storage contents ofsaid second virtual volume by copying data stored in said first cachememory to said second cache memory.
 11. The second storage controldevice according to claim 6, further comprising a second cache memorywhich is associated with said second virtual volume for temporarilystoring data to be stored in said second virtual volume, wherein saidsecond control unit reflects storage contents of said first virtualvolume in storage contents of said second virtual volume by directlycopying data written in said first virtual volume to said second cachememory.
 12. The second storage control device according to claim 6,wherein said real volume is present outside said second storage controldevice.
 13. The second storage control device according to claim 6,wherein at least either said first virtual volume said second virtualvolume is provided in a plurality.
 14. The second storage control deviceaccording to claim 6, comprising a plurality of said second virtualvolumes, these second virtual volumes respectively forming a pair withdifferent copy destination volumes.
 15. The second storage controldevice according to claim 6, wherein said first control unit, saidsecond control unit, and said third control unit are respectivelymounted on channel adapters for controlling data communication with ahost device.
 16. A data relay method using a storage control device fortransmitting data stored in a first storage control device to a thirdstorage control device via a second storage control device, comprisingthe steps of: setting a first virtual volume and a second virtualvolume, each being associated with a real volume, into said secondstorage control device; forming a first pair from said first virtualvolume and a copy source volume of said first storage control device;forming a second pair from said second virtual volume and a copydestination volume of said third storage control device; synchronizingstorage contents of said copy source volume and storage contents of saidfirst virtual volume; synchronizing storage contents of said firstvirtual volume and storage contents of said second virtual volume; andsynchronizing storage contents of said second virtual volume and storagecontents of said copy destination volume.